To access Castle Rock and its only route from Ketchum, Idaho, drive 22 miles northeast on Trail Creek Road, an improved gravel road, until reaching the turnoff for Wildhorse Creek and the Copper Basin.
Continue on Copper Basin Road, another improved gravel road, past the Wildhorse turnoff until bending a corner in which the unmistakable towers of Castle Rock boldly face the valley. Drive past the sign that identifies Castle Rock, yet does not give an elevation, until reaching the spot where Castle Creek flows into the East Fork Big Lost River. Park here.
The difficult river crossing near Castle Rock
It is important to know that access to Castle Rock is not possible until September due to the dangerous river crossing of the East Fork of the Big Lost River.
From the spot along Copper Basin Road where Caslte Creek flows into the Big Lost River, park and cross through the swampy terrain surrounding the river aiming toward the mouth of Castle Creek Canyon.
Look for remains of a faint trail that follow Castle Creek and hike to the point where a small drainage enters from the north at roughly 7,500'. Leave the trail and bushwhack up the marshy drainage to 7,800'.
From here, gain the tree-studded ridge that leads to the north ridge of Castle Rock by hiking up a small valley between two prominent rock towers. Once at the mellow evergreen forest, turn south and climb the increasingly steep terrain to the bottom of the cliffs that lead to Castle Rock's summit.
Once at the base of the cliffs, contour around them to the west side until reaching a small scree slope below sag-filled-face.
Climb up the small drop-off at the small of the face to gain a series of solid ledges above. It is class three terrain to until just below the crest of the ridge. On the north side of the face are two options, both of which border on class IV terrain.
Option one is a prominent crack in between two large boulders. At the top of the crack is an overhangin boulder that would make this option difficult for larger people. From the top of the crack, traverse across a small ledge that is exposed to the ridgeline above.
Option two is next to option one but has a few more footholds and is better use for a descent. To climb, follow the obvious, sturdy holds up the center of the chute.
At the top of either options, the summit and the south ridge become visible. Climb the small of the ridge a few dozen feet until coming to a wall that leads to the final gap below the true summit. Downclimb through a small crack in between two large boulders to the gap and use a well defined series of ledges to gain the windswept summit.
No technical gear required, just common sense and good route finding abilities.
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